package com.bestv.search.engine.compass.spellcheck;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermEnum;

import java.io.IOException;
import java.util.Iterator;

/**
 * Lucene Dictionary: terms taken from the given field of a Lucene index.
 * <p/>
 * When using IndexReader.terms(Term) the code must not call next() on TermEnum
 * as the first call to TermEnum, see:
 * http://issues.apache.org/jira/browse/LUCENE-6
 */
public class LuceneDictionary implements Dictionary {
    private IndexReader reader;
    private String field;

    public LuceneDictionary(IndexReader reader, String field) {
        this.reader = reader;
        this.field = field.intern();
    }

    public final Iterator getWordsIterator() {
        return new LuceneIterator();
    }

    final class LuceneIterator implements Iterator {
        private TermEnum termEnum;
        private Term actualTerm;
        private boolean hasNextCalled;

        LuceneIterator() {
            try {
                termEnum = reader.terms(new Term(field));
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }

        public Object next() {
            if (!hasNextCalled) {
                hasNext();
            }
            hasNextCalled = false;

            try {
                termEnum.next();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }

            return (actualTerm != null) ? actualTerm.text() : null;
        }

        public boolean hasNext() {
            if (hasNextCalled) {
                return actualTerm != null;
            }
            hasNextCalled = true;

            actualTerm = termEnum.term();

            // if there are no words return false
            if (actualTerm == null) {
                return false;
            }

            String currentField = actualTerm.field();

            // if the next word doesn't have the same field return false
            if (currentField != field) {
                actualTerm = null;
                return false;
            }

            return true;
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }
    }
}
